Ceramic tile burners having some degree of porosity can be used as flame holders and radiant heat sources in a variety of applications. Typically, a fuel stream including a fuel component and an oxidant component is introduced at an input face of a ceramic tile burner, where the fuel stream passes into channels or pores of the ceramic tile.
The prior art teaches that, depending upon the surface heat loading of the ceramic tile burner, the fuel stream may begin combusting while inside the porous tile, or may combust as it passes out of an output face of the porous tile. For example, U.S. Pat. No. 4,919,605, to Sarkisian, explains that at low surface heat loads, ceramic tiles act as radiant burners. Combustion of gaseous reactants . . . takes place within the ceramic tile, and the tile becomes radiant. Ignition of the incoming reactants is caused by the high temperature of the ceramic [tile].”
Increasing the surface heat loading results in increased velocity of the fuel stream. According to Sarkisian, at moderate surface heat loading rates, combustion takes place at or above the ceramic tile and the tile is cooled by the incoming reactants. In this regime, the ceramic tile acts as a . . . thermal barrier, and flame holder. Segments between the pores of the tiles cause turbulent recirculation zones to form, and this recirculation of hot gases ignites the combustion reactants as they exit the tile . . . . Increasing the surface heat loading . . . of a ceramic tile burner . . . produces very high velocity reactant flow when low porosity tiles are used . . . . With high porosity ceramic tiles, channel wall thicknesses are small. This has a detrimental effect on the formation of downstream recirculation zones. For this reason, the flame holding capabilities of the tiles are poor, resulting in unstable combustion.”
Thus, Sarkisian proposes a tile burner with a wire mesh positioned over the output face to act as a flame holder. Using this arrangement with a tile burner having a porosity of 70%, Sarkisian reports surface loading rates as high as 6500 BTU/H/in2 (0.94 MBTU/H/ft2).